I lost my very first ferret to a filter...I don't smoke, and my ex-
boyfriend wasn't supposed to smoke in the house, but did anyway
when I wasn't around. The thing that likely did the most damage
was the fact that it was an old, "used" filter. So not only did my
little boy's body have to deal with toxins from the blockage, but
also toxins in the filter, he made it through surgury, but not long
afterwards. If your ferret got a "fresh" filter, you would likely have to
worry less about that.

I am not a vet, but especially where tobacco was possibly injested,
if your ferret shows signs of being blocked, I would not wait to see
what happened. They can die very quickly, and my personal
feeling is I'd much rather take the risk of surgury when it appears
there's a blockage and there's nothing coming out, than wait until it
was perhaps too late.